The present invention relates to a programmable controlled-exposure radon measurement system for determining the level of radon gas and its daughter products at a selected test site.
Various devices have been developed for the purpose of measuring radon and other radioactive gas concentrations in residential and commercial buildings. Such devices include charcoal collectors, alpha-track detectors, and electret detectors. Representative electret detectors are disclosed in U.S. patent application Ser. No. 07/409,695, now U.S. Pat. No. 4,992,658, filed Sept. 20, 1989 and entitled "An Electret Ion Chamber for Radon Monitoring" and U.S. Pat. No. 4,853,536 issued Aug. 1, 1989 and entitled "Ionization Chamber for Monitoring Radioactive Gas." These detectors are of the integrating type in that they continuously measure the average concentrations of radon or other radioactive gases over a period a several days or weeks.
Recently, governmental agencies have sought to obtain radon measurements of buildings that are occupied only part of the time in an effort to obtain data that is more representative of actual occupant-exposure levels. For example, a continuous integrating monitor may not provide appropriate occupant-exposure data at school classroom test sites in which the classrooms are occupied for an 8-hour period each weekday and otherwise unoccupied. Some monitoring devices, such as those disclosed in the above cited documents, can be selectively inhibited and enabled to effect the desired occupant-exposure monitoring. While manual operation is suitable for small-scale testing, the labor requirement becomes larger for a large number of sites that must be simultaneously monitored. For example, the labor requirement to monitor all classrooms within a 1000 classroom school system is uneconomic, and the probability of the monitoring devices being enabled and disabled at the proper time is not high.